Lab-on-a-disc for ultrafast plasmonic assay of cysteamine

Cysteamine (CA) is a cystine depleting agent used in the treatment of cystinosis and many other diseases. However, high dose of CA can be toxic and thus point-of-care-test devices measuring blood CA level can be highly beneficial. Here, we report a highly sensitive, straightforward, and quantitative assay for the colorimetric and spectroscopic determination of CA concentration using plasmonic nanoparticles. The principle is based on the chemical etching-induced exchange of the surface ligands of plasmonic gold nanoparticles (AuNPs) upon the addition of CA. Moreover, destabilized particles can aggregate to generate the plasmonic couplings that trigger the redshift in the ultraviolet-visible (UV-vis) spectrum (the absorption band shifted from 526 to 732 nm) and the solution color change (wine-red to blackish-blue). This plasmonic AuNPs sensor displays a clear red-to-blue colorimetric transition in the presence of CA among various biothiols with high specificity and sensitivity within a short time (<15 s). Furthermore, a lab-on-a-disc platform was applied to the analysis of blood samples donated by healthy volunteers spiked with known amounts of the CA standard solution. This fully automated lab-on-a-disc platform approach for naked eye detecting the CA concentration in human blood samples (20 μL) is highly simple and time-efficient (<6 min), and it would be potentially useful for the careful selection of CA doses in the hospital industry.